Refractive surgery is a method of treating myopia, hyperopia, astigmatism, and other corneal abnormalities in human beings. This process involves reshaping a portion of the cornea, the transparent outer layer of the eye, to change its effective curvature. In recent refractive surgical methods, a preselected layer from the anterior surface of the cornea is removed in order to modify the tissue underneath. The corneal layer may be removed completely, as described in U.S. Pat. No. 4,840,175 issued to Peyman, but preferably the layer remains connected to the cornea as a hinged flap.
Included in refractive surgical methods is lamellar keratectomy, as described in U.S. Pat. No. 5,556,406 issued to Gordon et al., wherein a first layer of the cornea is raised, a second layer of the cornea may be removed, and then the first layer is replaced. Alternatively, laser intrastromal keratomileusis, or LASIK, procedures utilize a laser to reprofile the surface underlying the raised corneal layer in order to modify the corneal curvature, as described in U.S. Pat. No. 4,903,695 issued to Warner et al.
Different devices have been designed for performing refractive surgery on patients. One such device is a keratome, which has a motorized cutting blade for performing resections of the cornea. The blade in a keratome oscillates from side to side at high speed to cut the corneal tissue, while the blade is manually pushed or automatically driven in a path across the eye.
Keratomes typically include a suction ring, which is placed on the eye to position the cornea for cutting. In addition, a horizontal plate is assembled onto the suction ring. When placed over the eye, the suction ring draws the cornea therethrough to flatten it against the horizontal plate for slicing by the blade. Examples of such keratomes can be found in U.S. Pat. No. 5,586,980 issued to Kremer et al., U.S. Pat. No. 5,342,378 issued to Giraud et al., U.S. Pat. No. 5,595,570 issued to Smith, U.S. Pat. No. 5,624,456 issued to Hellenkamp, and U.S. Pat. No. RE 35,421 issued to Ruiz et al. The vertical spacing between the plate and the blade determines the depth or thickness of the cut. The setting of the blade is extremely critical, and the depth of the cut must be known precisely and accurately. For example, U.S. Pat. No. 5,288,292 issued to Giraud et al. discloses a keratome having a differential micrometer to adjust the depth of cut.
Due to their use of a horizontal plate structure, prior art keratomes have two main disadvantages. First, the horizontal plate obstructs an operator's view of the eye, preventing the operator from monitoring the corneal resection. As a consequence, an operator is not able to make informed decisions regarding altering or aborting the cut during the procedure. Second, keratomes are usually dependent on the use of a vacuum for proper functioning, in order to bring the cornea flat against the horizontal plate to position the cornea for cutting by the blade. However, a suction source is not always available, or may malfunction during the procedure. Furthermore, patients with high myopia have a tendency for retinal detachment, a condition which may be aggravated by the use of suction in this manner.